Isotope geochemistry of carbonate rocks

Strontium Isotope Stratigraphy (SIS) is an efficient way to date carbonate fossils. SIS has known a considerable evolution during the last decade. The improvement in precision of the analytical devices, the development of new high performance measuring facilities and their direct application in modern geology have brought the interpretation and comprehension of regional and local geology to a new level. The method is based on the hypothesis that the 87Sr/86Sr ratio of the global ocean waters is in equilibrium and underwent global secular variations with a général incérasse during the Phanerozoic. Minerals precipitated in normal marine waters record the marine 87Sr/86Sr ratio of the time of their formation. Still ongoing studies permit to refine the existing curve in order to be used as a precise dating method. In this research work, various carbonate rock and fossil samples from Central America will be studied. In a first place, measures of the 87Sr/86Sr value with a LA-ICP-MS and with a TIMS will be done in order to compare the different results obtained. The next step consists in maximizing the sensitivity and suppressing elemental fractionation of the LA-ICPMS device to measure 87Sr/86Sr as precisely and accurately as possible. Until now no comprehensive strontium isotope study on the Central American sedimentary rocks has been done and only few 87Sr/86Sr measures exist (Baumgartner-Mora et al. 2008).